【作者】 王静；

【导师】 焦明星；

【作者基本信息】 西安理工大学 ， 光学工程， 2019， 硕士

【摘要】 双波长单纵模光纤激光器是一种双频光纤激光器,除了具有光束质量高、振荡阈值低、转换效率高、温度稳定性好等光纤激光器的传统优点之外,还具有频差大、调谐方便等优势,可广泛应用于激光干涉测量、光纤传感、高速相干光通信和激光雷达探测等领域。尤其作为合成波绝对距离干涉测量系统的光源,为了实现长距离测量,必须保证双频激光具有足够窄的谱线宽度以获得足够长的相干长度。因此,开展双波长单纵模窄线宽光纤激光技术研究具有重要的意义。本论文设计了双波长单纵模窄线宽掺镱光纤激光器(YDFL)研究方案,即采用光纤偏振分束器并联双光纤布拉格光栅(FBG)实现双波长振荡,并利用未泵浦掺镱光纤(UPYDF)作为饱和吸收体实现单纵模选择,从而实现双波长单纵模激光振荡;在此基础上,采用光外腔弱反馈法,设计了两种不同外腔反馈结构以压窄激光线宽。论文的主要研究内容包括以下几部分:首先,概述了双波长单纵模窄线宽光纤激光器的研究现状,分析了掺镱光纤的特性和YDFL的工作原理;在分析多波长选择方法、单纵模选择方法和激光线宽压窄方法的基础上,设计了双波长单纵模窄线宽YDFL研究方案,理论计算了增益光纤的最佳长度、未泵浦掺镱光纤的最小长度和内嵌UPYDF光纤环臂长差的极限值;理论分析表明:当外腔长度在特定范围内,外腔反射率越大,激光线宽越窄。其次,建立了双波长单纵模YDFL实验系统,实验研究结果表明:这种双波长单纵模光纤激光器可以稳定振荡输出;通过控制偏振控制器可以切换激光器双波长或单波长运转,其开关特性良好;双波长单纵模激光器的阈值泵浦功率为58.52mW;双波长激光均为线偏振光。第三,建立以FBG反馈和耦合器分光反馈的两种不同外腔结构的驻波腔1064nm单频窄线宽YDFL系统。对于FBG反馈激光系统,当作为激光器内外腔镜的两个FBG的中心波长、带宽等参数一致时,可以实现线宽压窄,实验结果表明:当外腔长为160.3cm时,激光线宽从0.301pm压窄为0.273pm,线宽压窄比为9.11%;对于耦合器分光反馈激光系统,实验结果表明,当外腔长为320.2cm,激光线宽从0.301pm压窄为0.258pm,线宽压窄比为14.37%。综上所述,本论文设计的基于FBG反馈和耦合器分光反馈的双波长单纵模YDFL线宽压窄方案是可行的,该项研究为今后进一步开展双波长单纵模窄线宽光纤激光技术研究与应用奠定了坚实的基础。更多还原

【Abstract】 Two-wavelength single-longitudinal-mode fiber laser is a new implementation form of dual-frequency fiber laser.In addition to the traditional advantages of fiber lasers,such as high beam quality,low oscillation threshold,high conversion efficiency,good temperature stability,it also has the unique advantages of large frequency difference and convenient frequency tuning Two-wavelength single-longitudinal-mode ytterbium-doped fiber laser can be widely utilized in laser interferometric system,optical f-iber sensing,high-speed coherent optical communication and lidar detection.In particular,as a source of the synthetic wave absolute-distance interferometric system,it has a sufficiently narrow spectral line-width for a dual-frequency laser to achieve a sufficiently long coherence length for the long-distance measurement.Therefore,it is of great significance to research the techniques of two-wavelength single-longitudinal-mode fiber laser.In this thesis,the scheme of two-wavelength single-longitudinal-mode ytterbium-doped fiber laser(YDFL)with narrow line-width has been proposed.A parallel structure consisting of a fiber polarization beam splitter and double fiber Bragg gratings(FBGs)have been used to realize the oscillation of two-wavelength laser.An unpumped ytterbium-doped fiber(UPYDF)has been employed as a saturated absorber to achieve the selection of single-longitudinal-mode.Therefore,the two-wavelength single-longitudinal-mode laser oscillation can realize.On this basis,by adopting the method of extra-cavity weak feedback,double different extra-cavity feedback structures have been designed and been appli’ed to narrow the laser line-width.The main contents of the thesis are included as follows:Firstly,the research status of two-wavelength single-longitudinal-mode narrow-linewidth fiber lasers have been summarized,and the characteristics of ytterbium-doped fiber and the principle of YDFL have been analyzed.Based on the analyses of the multi-wavelength and single-longitudinal-mode selecting methods and laser line-width narrowing methods,a technical scheme of two-wavelength single-longitudinal-mode narrow-linewidth YDFL has been proposed.The optimal length of the gain fiber,the minimum length of the unpumped ytterbium-doped fiber and the limited value of the arm-length difference of the embedded UPYDF fiber ring have been theoretically calculated.The simulation results show that the extra-cavity reflectivity is larger,and the laser line-width is narrower,when the extra-cavity length is within a certain rangeSecondly,the experimental system of two-wavelength single-longitudinal-mode YDFL has been established.The experimental results show that the proposed two-wavelength single-longitudinal-mode fiber laser can realize the stable oscillation output.The double wavelengths or single wavelength operation of the laser can be switched by controlling the polarization controller?whose switching characteristic is reliable.The threshold pump power of a two-wavelength single-longitudinal-mode laser is 58.52mW.Both wavelengths are linearly polarizedThirdly,the system of 1064nm single-frequency narrow-linewidth YDFL has been established.The double different extra-cavity structures have been designed adopting the methods of FBG feedback and coupler splitting feedback,respectively.For the FBG feedback laser system,when the center wavelength and bandwidth of the double FBGs as the internal and external mirrors of the laser are the same,the laser line-width can be narrowed.The experimental results indicate that when the extra-cavity length is 160.3cm,the laser linewidth is narrowed from 0.301pm to 0.273pm,and the line-width narrowing ratio is 9.11%.For the coupler split-light feedback laser system,the experimental results indicate that when the extra-cavity length is 320.2cm,the line-width is narrowed from 0.301pm to 0.258pm,and the line-width narrowing ratio is 14.37%In summary,the simulation and experimental results prove the feasibility of the designed line-width narrowing scheme of dual-wavelength single-longitudinal-mode YDFL based on FBG feedback and coupler splitting feedback,which has laid a solid foundation for further research and application of two-wavelength single-longitudinal-mode narrow-linewidth fiber laser technologies.更多还原